ABSTRACT
Leishmaniasis is a parasitic infection that affects mostly
tropical and sub-tropical regions of the world and caused by diverse pathogens
that belong to the genus Leishmania. The pentavalent antimonials
developed in 1945 are still first line treatment drugs for both cutaneous
and visceral leishmaniasis while amphotericin B is a second line treatment
drug. These treatments come with toxic side effects even at effective doses and
the lack of vaccine demand the urgent need for new anti leishmanial agents.
This study aimed at investigating four plants used traditionally to treat
parasitic infections. The collected plant parts were washed, dried, powdered
and then extracted using ethanol. Different concentrations of the extracts
ranging from 15.6 to 500 µg/mL in 0.1 % DMSO with M199 and a positive control
of Amphotericin B were prepared in triplicates in 24-well plates that contained
117,000 parasites/well. The plates were incubated at 25 °C and promastigotes
counted on 8, 12, 24 and 48 hours after incubation. Phytochemical screening on
all crude extracts revealed the presence of steroids, triterpenoids, tannins,
anthraquinons, saponins, alkaloids, flavonoids and glycosides. Of the four
plants, Erythrophleum ivorense gave the best activity with an IC50 of
6.3 µg/mL after 72 hours. This was followed by C. oxycarpum, A. aubryanum
and A. ahia respectively. Three compounds have been isolated from E.
ivorense; erythroivorensin, eriodictyol and betulinic acid, with IC50s of
0.5, 61.8 and 247 µg/mL correspondingly on the promastigotes of L. donovani.
CHAPTER ONE
INTRODUCTION
Background
Leishmaniasis is an important
parasitic disease that threatens the lives of millions of people worldwide and
is caused by any of the numerous species of Leishmania (World Health
Organization, 2013). The worldwide increase in the incidence of leishmaniasis
has been mainly attributed to a surge in several risk factors that are clearly
manmade (Desjeux, 2001). The disease presents in several forms depending on the
type of species that is implicated and the immune response of the host
(Herwaldt, 1999). In some forms, it is lethal, while in others, it has been
described as a cruel mutilator leaving its victims scarred for life (Yanik,
Gurel, Simsek, & Kati, 2004).
Anti-leishmanial vaccines are still
being developed and as such the current control strategies for leishmaniasis
rely on case management case such as detection and treatment, vector and
reservoir control. Case management that includes early diagnosis and treatment
is essential for both individual patients and for the community. There is
reason to believe that the number of cases of leishmaniasis is on the rise
(Desjeux, 1996) which could be due to artificial environmental changes which
increase human exposure to the sand fly vector (Reithinger et al., 2007).
Extracting timber, mining, building dams, widening areas under cultivation, new
irrigation schemes, road construction, widespread migration from rural to urban
areas and fast urbanization worldwide are among the
main causes for an increased exposure to the sand fly (Reithinger et al.,
2007).
Several treatments are available
for the various groups of leishmaniasis. These drugs span from the ancient old
antimonies to the most current miltefosin. Because most of the treatment drugs
are old, their efficacy is limited presenting with several undesirable side
effects (Chakravarty & Sundar, 2010; Diro et al., 2014; Lage, et al.,
2013), making them far from satisfactory in their action even at the supposed
effective doses. Drugs that are recommended for use in the treatment of
cutaneous leishmaniasis and visceral leishmaniasis include the pentavalent
antimonials which were first introduced nearly seven decades ago (Yardley &
Croft, 2000). Over the past 20 years, alternative drugs or new formulations of
other standard drugs have been presented and registered for use in some
countries, whilst other drugs are on clinical trial for both forms of the
disease (Yardley & Croft, 2000). However, serious side effects in the
patients, prolonged treatment time, and increased parasite resistance have been
draw backs over the years (Chakravarty & Sundar, 2010; Diro et al., 2014;
Lage et al. 2013). Therefore, alternative drugs to the antimonials such as amphotericine
B, pentamidine, paromomycin, and miltefosine have been recommended, but they
also come with some problems and even therapeutic failure (Lage et al., 2013,
Machado et al., 2012; Wiwanitkit, 2012).
The use of herbal medicine for the
treatment of diseases and infections is as old as mankind (Surendra &
Talele, 2011). The World Health Organization supports the use of traditional
medicine provided they are proven to be efficacious and safe (Government of
India, 2001). In the developing countries,
vast numbers of people live in extreme poverty who suffer and die, for want of
medicine among others, and lack alternative for primary health care (GOI,
2001). Therefore, the need to use medicinal plants as alternatives to orthodox
medicines in the provision of primary health care cannot be over-looked. Herbal
medicines now seem to be the remedy for both traditional and modern medicine
(Zerehsaz et al., 1999). Additionally, herbal medicines have received much
attention as sources of lead candidate compounds since they are considered as
time tested and relatively safe for both human use and environmental friendliness
(Fazly-Bazzaz, Khajehkaramadin, & Shokooheizadeh, 2005), including easily available
and affordable. There is therefore, the need to look inwards to search for
herbal medicinal plants with the aim of validating the ethno medicinal use and
subsequently an isolation and characterization of compounds which will be added
to the potential lists of drugs.
Modern synthetic drugs for
leishmaniasis are simply not available or the few available ones are expensive
while some come with adverse side effects. To obtain herbal medicine or an
isolated active compound, different research strategies can be employed, among
them are; the investigation of the traditional use, the chemical composition,
the toxicity of the plants, or the combination of several criteria (Rates,
2001). For purification and isolation, the active extracts of the plant are sequentially
fractionated, and each fraction and/or pure compound can be evaluated for
biological activity and toxicity.
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